The present invention relates to a ceramic heater for heating semiconductor wafers (the workpiece to be heated), which is used in CVD apparatuses or sputtering apparatuses in the manufacturing process of semiconductor devices, or in an etching apparatus to etch away a thin film, for example.
A semiconductor wafer has to be supported by a fixing means when undergoing certain types of processing or when subjected to microscopic inspection, in order to prevent displacement or falling of the wafer held by a sample holder during the processing or inspection procedure. Mechanical chucks are used in the prior art as a supporting means, and, among them, vacuum chucks are preferred because they have the advantage of never sealing the surface of the sample. However, vacuum chucks cannot be used when the processing or inspection is performed under a reduced pressure or in a vacuum, and this has led to the development of electrostatic chucks (see Japanese Laid-Open Patent Application S52-67353). With an electrostatic chuck, the electrostatic chuck electrode unavoidably keeps a distance from the sample by intervention of an insulating layer.
It is a well known technology that, in the production of semiconductor devices, a polysilicon film, an oxide film, a conductor film, a dielectric film, or the like is formed on the semiconductor wafer with a CVD or sputtering apparatus, or that these thin films are etched with an etching apparatus. This technology requires that the semiconductor wafer (the workpiece under processing) be kept constant at a desired temperature in order to maintain the quality of the formation or etching of the thin films, and requires a heater (ceramic heater) for heating the semiconductor wafer in order to adjust this temperature to be kept constant.
In heating of a semiconductor wafer, the whole surface of the semiconductor wafer must be evenly fixed onto the heater, and an electrostatic attracting device (electrostatic chuck) is used in a reduced pressure atmosphere. As the process temperature is increasing in recent years, the material of the insulating layer is changed from synthetic resins to ceramics. For example, the materials used for the insulating layer include alumina, silica, and magnesia (see Japanese Laid-Open Patent Application S59-124140), as well as pyrolytic boron nitride (see Japanese Laid-Open Patent Application H7-10665).